This invention relates to apparatus for performing signaling functions in a digital communication system and more particularly to improved apparatus for performing asynchronous signaling in a digital communication channel.
The conventional method of communicating signaling information in a synchronous communication link or channel is to multiplex bits of a signaling word with channel information bits with due regard to the framing format. With synchronous signaling techniques the equipment defines when a signaling word is allowed to start and thus an inherent variable delay occurs between the time a random change to a different signaling message is desired and the time when it is completely received. Asynchronous signaling techniques, however, convey signaling messages at times that are not predictable, i.e., the receiver has no knowledge as to when a signaling word will start. Also since there is no transmission of any signaling information until a different signaling message is to be transmitted, failure of the asynchronous communication system can occur without the system being aware of this failure.
An object of this invention is the provision of improved apparatus for performing asynchronous signaling.
Another object is the provision of improved apparatus which continuously transmits digital signaling words and makes decisions as to the transmitted signaling word for each bit of signaling information and which does not require information as to the start or stop of a particular signaling word.